Negatively charged phospholipids influence the activity of the sensor kinase KdpD of Escherichia coli

Synthesis of the high-affinity K+-translocating Kdp-ATPase of Escherichia c oli, encoded by the kdpFABC operon, is regulated by the membrane-bound sens or kinase KdpD and the soluble response regulator KdpE. K+ limitation or a sudden increase in osmolarity induces the expression of kdpFABC. Due to the importance of Kt to maintain turgor, it has been proposed that KdpD is a t urgor sensor. Although the primary stimulus that KdpD senses is unknown, al terations in membrane strain or the interaction between KdpD and membrane c omponents might be good candidates. Here, we report a study of the influenc e of the membrane phospholipid composition on the function of KdpD in vivo and in vitro using various E. coli mutants defective in phospholipid biosyn thesis. Surprisingly, neither the lack of the major E. coli phospholipid ph osphatidylethanolamine nor the drastic reduction of the phosphatidylglycero l/cardiolipin content influenced induction of kdpFABC expression significan tly. However, in vitro reconstitution experiments with synthetic phospholip ids clearly demonstrated that KdpD kinase activity is dependent on negative ly charged phospholipids, whereas the structure of the phospholipids plays a minor role. These results indicate that electrostatic interactions are im portant for the activity of KdpD.